Grid coating for thermionic electron emission suppression
AssigneeVarian Associates, Inc.
InventorGeorge Miram
Life of this patent
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Abstract
In an electron gun having a control grid in contact with the face of the cathode, unwanted thermionic emission from the cathode can be effectively suppressed by applying a thin (1 micron) coating of boron nitride to the surface of the control grid. The boron nitride has low thermionic emission itself and, in addition, has an unusual ability to shed or eliminate any deposits of emissive material such as barium or its oxides which come in contact with the boron nitride layer. For optimum performance and longest lifetime, the boron nitride layer is applied over a pyrolytic graphite layer which may be the conductive grid itself.
Claims21
A grid-controlled electron source comprising, a thermionic cathode having an electron-emissive surface, a multi-apertured insulative layer, and a multi-apertured control grid overlaying said electron emissive surface, said control grid comprising a multi-apertured conductive layer which is electrically isolated from said thermionic cathode by said insulative layer, said insulative layer being bonded to said control grid, the surface of said conductive layer distal said cathode being coated with a layer of boron nitride whereby the flow of thermionic electrons from said thermionic cathode can be controlled by applying a selected potential difference between said cathode and said conductive layer, and thermionic electron emission from said grid is inhibited by said boron nitride layer.
A grid-controlled electron source comprising:
- a cathode capable of emitting thermionic electrons;
- a control grid adjacent and insulated from said cathode, having a surface distal said cathode and capable of emitting thermionic electrons;
- and
- a layer of boron nitride coating said surface, said layer being sufficiently thin to inhibit the emission of thermionic electrons from said surface, and to not behave as a pure insulator.
A thermionic bonded-grid-controlled electron source providing suppression of thermionic emission by said grid, comprising:
- a thermionic cathode having an electron-emissive surface;
- a multi-apertured conductive grid overlaying said electron emissive surface;
- an insulative member interposed between said emissive surface and said conductive member;
- a barrier layer interposed between said insulative member and said emissive surface;
- and a boron nitride layer coating the surface of said conductive layer distal said cathode, said layer being much less thick than said insulative member to preclude said layer from behaving as a pure insulator, said layer inhibiting thermionic emission by said conductive layer, said cathode, grid, insulative member and barrier layer comprising a bonded unit,
- whereby thermionic electron emission from said cathode may be controlled by application of a selected potential between said conductive layer and said cathode, minimal cathode-to-grid spacing is provided, while thermionic emission from said grid is inhibited.
Dependencies are inferred from the claim text.